Caught in the Act!

 Beyoncé and Jay-Z, double-dating with Gwyneth Paltrow and Chris Martin at Madeo Restaurant in Beverly Hills. The couples met for
dinner after the BET Awards and were "definitely having a good time and
laughing," an onlooker tells us. At one point, the group switched seats so
the ladies could sit next to each other in the booth while the guys sat on
the outside.

 Meanwhile, also at Madeo, Matt Damon and wife
Luciana were eating with Jeremy Piven and a group of 10
friends. "Lucy was sitting next to another woman, chatting it up," the
onlooker tells us. The whole group toasted, raising their wine glasses at
one point. Meanwhile, Damon ate pasta and Piven opted for a veal dish.

 Megan Fox and on-again beau Brian Austin Green, attending the 7 p.m. performance of Cirque du Soleil's Mystère at Las Vegas's Treasure Island Hotel and Casino. Accompanied by the
actress's sister and her boyfriend, the group arrived via a black stretch
limo and stepped into the theater just as the show began. Fox and her
friends ate popcorn through the performance, then headed to dinner at
Mandalay Bay's Red Square restaurant.

 Rihanna, waiting in an Escalade with tinted
windows until her booth was ready at Beverly Hills restaurant Kate
Mantilini. Accompanied by three women, the R&B star sported a black blazer,
tiny jean shorts and leather boots and looked "gorgeous in person," an
onlooker says. The group sat in their booth for about an hour, eating
rotisserie chicken and sipping on bottled water.

 Mariah Carey and hubby Nick Cannon,
partying at The Eldridge in New York as Cannon played deejay for the
evening. "They were so cute," a fellow reveler tells us, adding that the
happy duo sipped champagne during their evening out.